Half Marathon Calculator

A half marathon is 21. 0975 km (13

The calculator uses the standard published formula for half marathon is 21. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

This calculator works with inches, kilometres, miles, kilometres per hour. You can enter values in the units shown — the calculator handles all conversions internally.

The core formula is: Pace per km (sec) = Total seconds / 21.0975. Each step in the calculation is shown so you can verify the result manually.